1. Field of the Invention
Apparatuses consistent with the present invention relate to a reference voltage generating circuit, and more particularly, to a reference voltage generating circuit capable of generating a plurality of reference voltages with ultra-low power consumption.
2. Description of the Related Art
Generally, a reference voltage generating circuit generating a reference voltage stably is required to adjust a high level voltage or provide internal power supply. To this end, the reference voltage generating circuit should be able to stably output a reference voltage of a uniform magnitude, independently of changes in external power supply, temperature, process, etc.
FIG. 1A and FIG. 1B are explanatory diagrams of an operational method of a reference voltage generating circuit according to a related art. Referring to FIG. 1A, a voltage VBE between the base and the emitter of a bipolar junction transistor (BJT) changes by temperatures, and operates as a CTAT (Complementary To Absolute Temperature) voltage.VBE=−2.2 mV/T  [Equation 1]
Therefore, as expressed in the following Equation 2, a voltage proportional to temperature is amplified to a predetermined magnitude (with reference to FIG. 1A), and added to the voltage VBE between the base and the emitter to generate a fixed magnitude of a reference voltage, VREF=KVt+VBE.
                                          Δ            ⁢                                                  ⁢                          V              BE                                =                                    V              T                        ⁢            1            ⁢            nm                          ;                              V            T                    =                                    KT              q                        =                          0.085              ⁢                                                          ⁢              mVT                                                          [                  Equation          ⁢                                          ⁢          2                ]            
That is to say, as shown in FIG. 1B, a temperature-independent voltage with a fixed magnitude can be generated by adding a VBE between the base and the emitter of the BJT and a PTAT (Proportional To Absolute Temperature) voltage. Similarly, a reference voltage generating circuit generating a fixed magnitude of voltage independently of temperature change can be configured.
However, a drawback of the above-described reference voltage generating circuit is that its total size may be increased by resistance used because a reference voltage is generated using transistors and resistance. Also, to obtain a reference voltage, a VBE between the base and the emitter and a PTAT voltage should be measured and added. This, however, provides only one single reference voltage, and consumes a large amount of current overall.
FIG. 2 is a circuit diagram illustrating one example of a reference voltage generating circuit according to a related art. In particular, the circuit in FIG. 2 is used for a Low Noise Micropower Precision Reference chip such as ADR290 manufactured by Analog Device Inc., and an output voltage thereof satisfies the following.
                              V          out                =                              Δ            ⁢                                                  ⁢                                          V                P                            ⁡                              [                                                                            R                      ⁢                                                                                          ⁢                      1                                        +                                          R                      ⁢                                                                                          ⁢                      2                                        +                                          R                      ⁢                                                                                          ⁢                      3                                                                            R                    ⁢                                                                                  ⁢                    1                                                  ]                                              +                      IPATER            ⁢                                                  ⁢            3                                              [                  Equation          ⁢                                          ⁢          3                ]            
The reference voltage generating circuit illustrated in FIG. 2 consumes lower power because it uses a field-effect transistor (FET) instead of a transistor, yet is capable of generating a stable reference voltage. But still, it consumes 12 μA, meaning that it cannot be used in an ultra-low power system like RFID whose total power consumption is only several μA. Similar to the previous example, this type of reference voltage generating circuit also supplies only one single reference voltage, and cannot supply a reference voltage required for bias or start-up.